1. Field of the Invention
The present invention relates to a lens barrel using a surface wave motor for driving a photographing lens by the use of the surface wave motor.
2. Related Background Art
Traditionally, in a lens barrel using a surface wave motor, the contacting faces of the rotor and stator are strongly pressurized due to the driving principle of the surface wave motor. It is therefore necessary to rotate the rotor with a torque greater than the friction exerted between the rotor (moving body) and the stator (fixed body) when the photographing lens should be driven manually.
As a method of performing the manual driving of the photographing lens with ease, there has been known a first method in which the friction exerted between the rotor and stator is weakened (Japanese Patent Laid-Open Application No. 59-101608) or a second in which the rotor and stator are set apart.
Also, there has been proposed a third method in which the moving body and fixed body of a surface wave motor are integrated for driving the photographing lens by interlocking its rotation with the manual operation of a manual operation member when a mode switching means is in manual mode and in which the fixed body is fixed to the lens barrel for driving the photographing lens by the rotation of the moving body in automatic mode, so that the photographing lens is driven without causing any damage on the contacting faces of the moving body and fixed body when a manual operation is performed (Japanese Patent Laid-Open Application No. 61-86718).
In the first method, although the friction is weak, the rotor is rotated in a state where it is still frictionally in contact with the stator. As a result, the contacting faces of the rotor and stator are caused to be worn unnecessarily. Also, in the second method where the rotor and stator are set apart, dust particles and the like are admitted between the rotor and stator, and a problem is encountered in that when the surface wave motor is driven, the contacting faces thereof are damaged due to such dust particles.
In the third method (disclosed in Japanese Patent Laid-Open Application No. 61-86718), friction is exerted on the contacting faces of the outer barrel of a surface wave motor and a fixed barrel so that the fixed body of the surface wave motor is not rotated in the fixed barrel even when a lens holding barrel is driven by the surface wave motor in the automatic mode, which is obtainable by sliding a switching means, whereas in the manual mode, which is obtainable by sliding the switching means in the opposite direction, the friction exerted on the contacting faces of a manual ring and outer barrel is mechanically switched to be greater than the driving power which drives the lens holding barrel. It is therefore necessary to provide a complicated mechanism for this method.
Also, when the so-called manual mode preference photographing is attempted, in which the manual operation ring is rotated while photographing in automatic mode to switch it to manual mode instantaneously, or when the so-called go-home photographing function is applied, in which an arbitrary distance is stored in advance and the photographing lens is driven by the stored photographic distance subsequent to a photographing at another photographic distance, some mechanical switching system is required. However, it is extremely difficult to build in such a mechanism that can rapidly execute the switching for the manual mode preference photographing, go-home photographing function, or the like.